Drilling tool and bearing system

ABSTRACT

A bearing system in an annulus between a shaft and a housing comprising a seal means in the annulus and bearing means on either side of the seal means, one of the bearing means having a piston means associated therewith to provide a lubricant reservoir which is sealed from external pressures and which will vary in volume depending upon the amount of lubricant present. A downhole drilling tool employing the above bearing system together with a downhole motor operably connected to the shaft of the bearing system, the other end of the shaft being adapted to carry a drilling bit.

United States Patent 19] Striegler [4511 May 1, 1973 [5 DRILLING TOOL AND BEARING 3,149,685 9 1964 Mitchell et al. ..175/107 SYSTEM 3,659,662 5/1972 Dicky ..175 107 7/ I 96! Works Primary Examiner-David H. Brown Attorney-Blucher S. Tharp et a].

A bearing system in an annulus between a shaft and a housing comprising a seal means in the annulus and bearing means on either side of the seal means, one of the bearing means having a piston means associated therewith to provide a lubricant reservoir which is sealed from external pressures and which will vary in volume depending upon the amount of lubricant present. A downhole drilling tool employing the above bearing system together with a downhole motor operably connected to the shaft of the bearing system, the other end of the shaft being adapted to carry a drilling bit.

ABSTRACT 9 Claims, 2 Drawing Figures Patented May 1, 1973 2 Sheets-Sheet l ,FIG./

& IN.

INVENTOR JOHN H. STRIEGLER I ATTORNEY Patented May 1, 1973 INVENTOR:

JOHN H. STRIEGLER 2 She et s-Shee t 2 Generally, when drilling a well bore in the earth weight is applied to a dt'lllbit and the bit is rotated to form the well bore. The weight is applied to the drill bit from the drill collar portion of a drill string containing drill pipe also. The drill string extends to the earths surface and the bit is rotated by rotating this drill string. The source of power for rotating the drill string is at the earths surface so that the rotational speed of the bit and the torque applied to the bit are transmitted from the earths surface through the drill string to the bit. The deeper the well bore, the further the bit is from the power source on the earths surface and the greater the loss of energy between the power source and the bit. Accordingly, the drilling operation becomes more inefficient as the well bore becomes deeper and the drill string longer.

It is desirable in such situations to have the power source for rotating the bit as close as possible to the bit itself and downhole motors have been devised which can be carried at the end of the drill string nearest the bit so that the distance between the power source and the bit is independent of well bore depth.

When using a downhole motor to rotate a bit, a shaft for rotating the bit interconnects the downhole motor and bit, but the weight applied to the bit still comes primarily from the drill string so that a critical subassembly in any tool which employs a downhole motor is the bearing system which will transmitthe weight from the drill string to the bit while the bit is being rotated by the downhole motor. The downhole bearing system, therefore, must transmit both radial forces which are at an angle to the longitudinal axis of the drill string and the downhole drilling tool and longitudinal forces which are generally parallel to the longitudinal axis of V the drill string and drilling tool.

The downhole bearing system must be very rugged and durable in that it transmits thousands of pounds of weight from the drill string to the bit even while the bit is rotating at a very high rate and because time and money are lost if the drilling has to be stopped due to a breakdown of the bearing system before the bit itself hasbeen worn out.

Generally, the bearing systems in downhole drilling tools are lubricated by the drilling fluid itself. Relying upon drilling fluid as alubricant for bearings can be unsatisfactory because drilling fluid, when performing one of its major functions of washing rock cuttings from thearea of the bit upwardly and out of the well bore,-picks up fine solid particles all of which are not separated from the drilling fluid at the earths surface before the drilling fluid is again passed down interior of the drill pipe string forreuse. Thus, rclyingupon a drilling fluid which contains suspended solid particles can reduce bearing life substantially assuming constant bit weightand constant conventional drilling conditions.

This adverse effect on bearing life is exaggerated to the critical point in that area of the drilling field known as slim hole" drilling wherein a borehole of small diameter, e.g., up to about 6 inches, preferably from about 2 to about 4 inches, is drilled while rotating the bit at very high rates of at least about 400 rpm, generally from about 400 to about 3000 rpm. Also, in

slim hole drilling, because of the restricted borehold diameter, it is much more difficult to get downhole bearings which will hold up under the necessary drilling bit weight. Q

Thus, in both conventional and. slim hole drilling, it is very desirable to have a downhole drilling tool and bearing system which excludes drilling fluid from the bearings themselves rather than relying upon the drilling fluid to lubricate the bearings.

SUMMARY OF THE INVENTION According to this invention, there is provided a well drilling tool for use downhole which employs a downhole motor means with a hollow shaft connected to a bit, a housing carried about the shaft and spaced therefrom to provide an annular chamber between the housing and shaft, the chamber containing a first seal means between the housing and shaft near the bit end and a second seal means in the chamber with first and second bearing means disposed on either side of the second seal means, and a piston means in the chamber which seals both bearing means from the remainder of the chamber, the shaft having an aperture therein so that the drilling fluid in the chamber can pass into the interior of the shaft upstream of the piston.

There is also provided a bearing system comprising the two seal means, two bearing means, and piston means mentioned hereinabove and described in greater detail hereinafter. Accordingly, it is an object of this invention to provide a new and improved bearing system. It is another object to provide anew and improved bearing system for use in downhole drilling tools. It is another object to provide a new and improved bearing system for use in a downhole drilling tool in conjunction with a downhole motor wherein the bearing system excludes entry of drilling fluid into the bearings. It is another object to provide a new and improved bearing system for use in a downhole drilling tool which contains its own lubricant in a sealed mannerso that fluids external to the system cannot enter nor contact the bearings in thatsystem. It

is another object to provide a new and improved well drilling tool for'use downhole in a wellbore to rotate a bit and to transmit weight from the drill string to the bit during drilling. It is another object to provide a new and improved downhole drilling tool which as a bearing system which will not permit the entry of drilling fluid and which contains its own lubricant. It is another ob-, ject to provide a well drilling tool whichcan be carried on a lower end of a drill string and which will rotate the bit at high speed while transmitting weight to the bit from the drill string.

Other aspects, objects and advantages of this invention will be apparent to thoseskilled in the art from this disclosure and the appended claims.

DETAILED DESCRIPTION or THE INVENTION motor means (not shown) and which, when rotated, in turn rotates square kelly 4. Kelly 4 is coupled by means of coupling 5 to drill string 6 which is normally composed of a plurality of individual sections of drill pipe coupled together by couplings such as coupling 5. Drill string 6 is coupled by means of coupling 7 at its lower end to downhole tool 8 which in turn carries diamond drill bit 9 on shaft 10.

In operation, rotary table 3 is rotated by a surface motor means to rotate, respectively, kelly 4, drill string 6, tool 8 and bit 9. Tool 8 is then operated on its own to speed up the rotation of bit 9 to any desired rate for the particular drilling condition.

In the case of slim hole drilling, if the very high rotational rate for the bit were to be achieved solely by rotating drill string 6 with a surface motor, catastrophic vibration of drill string 6 could be encountered. At high rotational speeds of a long drill string, the pipe tends to bounce from one side of the well bore to the other at a faster and faster rate until catastrophic vibration sets in and results in failure of the drill string such as by twisting off one section of drill pipe from an adjacent section of drill pipe at their common coupling joint. By use of the apparatus of this invention, drill string 6 can be rotated by rotary table 3 at a rate which avoids catastrophic vibration. However, the bit is still rotated at slim hole rotation rates by operation of downhole tool 8. Thus, the bit can be rotated a first speed increment using downhole tool 8 and further additional rotating speed of the bit accomplished by an additional speed increment provided by a surface motor means rotating drill string 6.

Downhole tool 8 can be located substantially any place along the length of drill string 6 but is preferably closer to the bit than the earthsurface when the borehole is deeper than the total length of the bit and the tool 8. Tool 8 is generally located adjacent the bit as shown in FIG. 1. It should be understood, however, that one or more tools 8 can be employed and can be spaced upwardly from the bit along the length of the drill string as desired.

Generally, any conventional downhole motor means can be employed in tool 8. Such motor means are commercially available and well-known in the art. These motors include downhole electric motors, turbine operated motors such as the turbo drill" wherein the drilling mud passing downwardly through the interior of the drill string runs a turbine and the turbine turns a shaft connected to the drill bit, or motors which are in reality a fluid pump in reverse such as the dyna-drill. Construction and operation of fluid-pump-in-reverse motors are fully and completely disclosed in U. S. Pat. No. 3,1 12,801 the disclosure of which is incorporated herein by reference. Generally, these motors have a stator and rotor which, at least when in operation if not otherwise, operate in relation to one another and are connected to one another by way of frictional forces including fluid friction as well as mechanical friction, or an electrical field, so that torque can be transmitted from the drill string 6 to the shaft which connects the downhole motor to the bit. In this way, rotational speed of the drill string 6 caused by operation of rotary table 3 can be transmitted to and added to the rotational rate output of the downhole motor thereby giving a cumulative total rotation rate to the bit which isgreater than the individual rotation rates of the drill string'6 and the downhole motor.

FIG. 2 shows a partial cross-sectional interiorof tool 8 and shows bit 9 to threadably engage hollow shaft 10 which in turn engages shaft 20. Shaft 20 is powered by a downhole motor means (not shown). Shaft 10 can engage shaft 20 in any manner such as by a plurality of splines on shaft 20 engaging a plurality of matching slots 21 in shaft 10. Shafts 10 and 20 can be made integral but are preferably separable for ease of replacement of the downhole motor.

Shaft 20 has one or more apertures 22 therein which serve as means to pass drilling fluid around the bearings by admitting drilling fluid from outside the shaft into the interior of the shaft as shown by arrow 23, the drilling fluid then passing down the interior of the shaft through the interior conduit 24 of bit 9 and out around the outer surface of bit 9 as shown by arrow 25 to cool the bit and sweep rock cuttings away from the bit. The rock cuttings are carried upwardly in the annulus by the drilling fluid between the walls of the well bore and the outer surface of drill string 6 to the surface of the earth where most of the cuttings are removed and the drilling fluid then returned down the interior of drill string 6 for reuse.

Annular housing 26 is concentric with and external to shaft 10 thereby providing an annular chamber 27 between the exterior of shaft 10 and the interior of housing 26. The upper end of housing 26, i.e., the end furthest removed from bit 9, is threaded so as to be connectible to the lower end of drill string 6 by way of coupling 7. I

The end of housing 26 closest to bit 9 touches or is at least quite close to shaft 10 but is slidable around and along shaft 10, i.e., not fixed by welding, bolting, or the like to shaft 10, so that shaft 10 can rotate independently of housing 26.

Annular chamber 27 is divided into three distinct sections. The upper section 30 contains the first bearing means, the middle section 31 contains the second seal means, and the third section 32 contains both the second bearing means and the first seal means.

Section 32 carries annular first seal means 33 which rotates with shaft 10 but bears against the interior wall of housing 26 thereby providing a dynamic seal between shaft 10 and housing 26 so that drilling fluid outside housing 26 cannot pass into chamber 27 and lubricant cannot leak out of housing 26 at this point even though housing 26 and shaft 10 are not physically joined to one another at this point. Above first seal means 33 is an annular spacer means 34 upon which rests lower annular race 35 of roller bearing- 36. Bearings 36 are disposed horizontally to transmit thrust forces acting substantially parallel to the longitudinal axis of shaft 10 in either direction, i.e., toward or away from bit 9. Upper annular race 37 confines the plurality of roller bearings 36 and completes the thrust bearing device for section 32. Above race 37 is disposed a grease fitting 38 for admitting lubricant to the interior of section 32. Shoulder 38' transmits bit weight from roller bearings 36 to housing 26.

Above fitting 38 is disposed ball bearings 39 between opposed annular races 40 and 41. This ball bearing device transmits radial forces which act at an angle to the longitudinal axes of shaft 10 and housing 26.

Section 32 therefore contains two bearing devices for transmitting radial and thrust forces. It also contains a substantial amount of open space which serves as a lubricant reservoir after the lubricant has been injected by way of fitting 38. To insure that there is an evenness of lubrication for both bearing devices in section 32, one or more conduit means 42 is provided through housing 26 and is in open communication with open areas adjacent roller bearings 36 and above roller bearings 39. Since roller bearings 36 force lubricant outwardly toward housing 26 by centrifugal force, lubricant circulates from the vicinity of roller bearings 36 through conduit means 42 and past ball bearings 39 back to roller bearings 36. In this manner, not only is a reservoir of lubricant provided in the interior section 32, but circulating means is provided so that uniform lubrication of all bearing devices in section 32 is maintained. o

Section 31 contains a second seal means which is composed of a lower, metal,.annular, support member 50and an upper, metal, annular, support member 51 which together define an open annular space 52 that is partially filled with a resilient, annularseal member 53. Seal member 53 is alip seal in that annular lip portion S4 is bendable toward and away from shaft as opposed to a face seal, e.g., seal 33, where the sealing surface is not bendable in the manner of lip 54. Members 50, 51 and 53 are carried by housing 26 so that when housing 26 is stationary these members are also stationary even though shaft 10 may be rotating. This second seal means is a dynamic seal means which bears upon shaft 10 whether both shaft 10 and housing 26 are stationary or either or both are moving. The lip portion 54 of resilient member 53 which contacts shaft 10 is pointed upwardly toward section 30 so that pressurized fluid which may enter space 52 from section 30 will force member 54 more firmly against shaft l0 thereby effectively sealing section 30 and its contained pressure from section 32 and its contained pressure even though the two contained pressures are substantially different I from one'another. Member 53 can be carried by shaft 10 or housing 26, preferably housing 26, and can be composed of any elastic material. Particularly rubber.

The elastic material can be impregnated with a lubricant such as a solid lubricant, e.g., graphite, M08 etc., so that as the elastic portion of the lip is worn away fresh lubricant is exposed to shaft 10. Member 53 also contains a plurality of layers of fibers, one or more of the layers being composed of a porous material such as cotton or rayon which will act as a wick in picking up and holding liquid lubricant inside member 53, and one or more layers of fibers that have a tensile strength greater than the wick fiber, e.g., nylon, polypropylene,

. etc., to to strengthen member 53 and particularly lip 6 units can be employed in section. 31 if desired. For example, from oneto ten of these. units stacked on top of one another in section 31 can be employed as a dynamic seal which effectively isolates the pressures in sections 30 and 32 from one another.

immediately above the last member 51 in section 31 is annular spacer 60which seals the pressure in section respect to one another so that roller bearings 65 will moving nut 71 the position of race 66 with respect to roller bearings 65 can be adjusted. Grease fitting 73 is provided so that lubricant can be injectedinto the interior of section 30 for lubrication of the bearing device therein. l

The upper end of section 30ris defined bya piston means 80 which is both rotatable and movablelongitudinally parallel to the longitudinal axis of shaft 10. Piston 80 seals the interior of section 30 from the upper remaining portion of chamber 27 in the vicinity of aperture 22 by way of O-rings 81 and 82. Any desired arrangement of O-rings can be employed so long as a dynamic sealing effect is achieved. Of course, sealing means other than O-rings can be employed so long as the desired moving-sealing results are realized. Piston 80 can move toward lock nut 71 or away from lock nut 71 thereby decreasing or increasing the volume between piston 82 and roller bearings 65, respectively.

This movement depends upon the amount of lubricant FIG. 2, comprise a single unit and a plurality of these present in that space. Thus, when the lubricant in that space decreases, the pressure from the drilling fluid above piston 80 pushes that piston downwardly toward lock nut thereby forcing all available lubricant just described since most of the elements are annular and extend completely around annular chamber 27. I

In operation, the downhole motor is energized by electricity, drillingfluid energy, etc., thus rotating shaft 20 and in turn rotating shaft 10 and bit 9. Drill string 6 may be stationary or rotating at the'same or lesser rate of rotation as shaft 10. In any of these cases roller bearings 65 and ball bearings 39 transmit some radial forces between shaft 10 and housing 26. Drilling fluid pumped down the interior of the drill string 6 passes into chamber 27 and is at a pressure P, in chamber 27 and in the interior of shaft 10. There is a pressure drop through bit 9 so that the drilling fluid emerging from the bottom of bit 9 is at a lower pressure P this lower section 32 is P, and even though P can be substantially less in magnitude than P the greater pressure is maintained in section 30 and the lesser pressure maintained in section 32 by way of the second seal means in section 31. It can be seen that drilling fluid above piston 80, inside shaft 10, and outside housing 26 (even where housing 26 adjoins shaft 10 in the vicinity of first seal means 33), is completely excluded from reaching any of the bearing devices in sections 30 and 32 and that the bearing devices in sections 30 and 32 are provided with their own self-contained reservoir of high grade lubricant. Thus, bearing life potential is maximized by 1 sealing all bearings in high grade lubricant and by excluding solid particle-containing drilling fluid from all the bearings. I

It can be seen that the second seal means in section 31 is the main seal of the two since it holds the pressure differential between P, and P Second seal means can be any rotating seal which can hold a pressure differential of from about 500 to about 800 psig at a shaft 10 rotation of I500 rpm. It can further be seen that the main thrust bearing device is that which contains roller bearings 36 since it transmits the weight on the bit as provided by drill string 6 less the much smaller down thrust due to the drilling fluid pressure drop across the downhole motor, if any.

,The combination bearing device in section 30, on the other hand, carries the pressure down thrust toward bit 9, if any, when it is greater than the bit weight provided by drill string 6. The combination bearing in section 30 also functions as a radial bearing together with the ball bearings 39 to maintain precise running alignment between shaft 10 and housing 26. Of course, more than one bearing device can be employed in section 30 and only one bearing device can be employed in section 32, or any combination of various bearing devices can be used in either section so long as the desired results are achieved. Bit 9 can be any conventional drilling bit, such as a diamond bit, rotary bit, insert bit, and the like.

Reasonable variations and modifications are possible within the scope of this disclosure without departing from the spirit and scope of this invention.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

l. in a well drilling tool whereby a drill bit is rotated in the earth to drill a well bore, the improvement comprising a downhole motor means, a shaft means connected at one end to said motor, the other end of said shaft being adapted to carry a drill bit, a housing carried concentric with said shaft and spaced therefrom thereby providing an annular chamber between said housing and said shaft, first'seal 'meansbetween said housing and shaft near the end of said housing closest to said bit, second seal means in said chamber and spaced from said first seal means, first bearing means between said second seal means and the end of said housing furthest from said bit, a movable piston means between said first bearing'm'eans and the end of said housing furthest from said bit, said piston being spaced from said first bearing means to provide a lubricant reservoir for said first bearing means which is sealed from the remainder of said chamber by said piston, second bearing means intermediate said first and second seal means, the space between said first and second seal means which contains said second bearing means providing a lubricant reservoir which is sealed from the outside of said housing and from the part of said chamber which contains said first bearing means, and means for passing drilling fluid from said chamber around said bearing and seal means to said bit.

2. A tool according to claim 1 wherein each of said first and second bearing means contains at least one bearing device.

3. A tool according to claim 1 wherein said first and second seal means are dynamic seals which seal against a rotating surface, said first seal means sealing against said housing when said housingis stationary or rotating, said second seal means sealing against said shaft when said shaft is stationary or rotating, and said piston is movable both rotatably and longitudinally in said chamber and serves as a dynamic seal between said housing and shaft when either or both said housing and shaft are stationary or rotating.

4. A tool according to claim 1 wherein said second seal means has at least one flexible sealmember that bears against said shaft pointing toward said first bearing means so that pressure acting from the area of said first bearing means toward said second bearing means forces said flexible seal member more firmly against said shaft.

5. A tool according to claim 1 wherein said first bearing means comprises at least one roller bearing device with the rollers disposed at an angle between the longitudinal and transverse axes of said shaft so that said first bearing means transmits both thrust and radial forces, said second bearing means comprises at least one ball bearing device for transmitting radial force and at least one roller bearing device for transmitting thrust force, and conduit means associated with said second bearing means for the circulation of lubricant between said roller bearing device and said ball bearing device, and said means for passing drilling fluid from said chamber around said bearing and seal means to said bit comprises said shaft being hollow and having at least one aperture therein located to admit drilling fluid to the interior of said shaft upstream of said piston.

6. A tool according to claim 4 wherein said first bearing means is positioned to transmit thrust forces which act to force said shaft out of said housing in the direction of the bit end of said shaft and said at least one roller bearing device of said second bearing means is positioned to transmit thrust forces acting in either direction along the longitudinal axis of said shaft.

7. A tool according to claim 1 wherein said second seal means comprises at least one elastic lip seal, said lip seal being supported by metal support members, said lip seal being impregnated with lubricant. 

1. In a well drilling tool whereby a drill bit is rotated in the earth to drill a well bore, the improvement comprising a downhole motor means, a shaft means connected at one end to said motor, the other end of said shaft being adapted to carry a drill bit, a housing carried concentric with said shaft and spaced therefrom thereby providing an annular chamber between said housing and said shaft, first seal means between said housing and shaft near the end of said housing closest to said bit, second seal means in said chamber and spaced from said first seal means, first bearing means between said second seal means and the end of said housing furthest from said bit, a movable piston means between said first bearing means and the end of said housing furthest from said bit, said piston being spaced from said first bearing means to provide a lubricant reservoir for said first bearing means which is sealed from the remainder of said chamber by said piston, second bearing means intermediate said first and second seal means, the space between said first and second seal means which contains said second bearing means providing a lubricant reservoir which is sealed from the outside of said housing and from the part of said chamber which contains said first bearing means, and means for passing drilling fluid from said chamber around said bearing and seal means to said bit.
 2. A tool according to claim 1 wherein each of said first and second bearing means contains at least one bearing device.
 3. A tool according to claim 1 wherein said first and second seal means are dynamic seals which seal against a rotating surface, said first seal means sealing against said housing when said housing is stationary or rotating, said second seal means sealing against said shaft when said shaft is stationary or rotating, and said piston is movable both rotatably and longitudinally in said chamber and serves as a dynamic seal between said housing and shaft when either or both said housing and shaft are stationary or rotating.
 4. A tool according to claim 1 wherein said second seal means has at least one flexible seal member that bears against said shaft pointing toward said first bearing means so that pressure acting from the area of said first bearing means toward said second bearing means forces said flexible seal member more firmly against said shaft.
 5. A tool according to claim 1 wherein said first bearing means comprises at least one roller bearing device with the rollers disposed at an angle between the longitudinal and transverse axes of said shaft so that said first bearing means transmits both thrust and radial forces, said second bearing means comprises at least one ball bearing device for transmitting radial force and at least one roller bearing device for transmitting thrust force, and conduit means associated with said second bearing means for the circulation of lubricant between said roller bearing device and said ball bearing device, and said means for passing drilling fluid from said chamber around said bearing and seal means to said bit comprises said shaft being hollow and having at least one aperture therein located to admit drilling fluid to the interior of said shaft upstream of said piston.
 6. A tool according to claim 4 wherein said first bearing means is positioned to transmit thrust forces which act to force said shaft out of said housing in the direction of the bit end of said shaft and said at least one roller bearing device of said second bearing means is positioned to transmit thrust forces acting in either direction along the longitudinal axis of said shaft.
 7. A tool according to claim 1 wherein said second seal means comprises at least one elastic lip seal, said lip seal being supported by metal support members, said lip seal being impregnated with lubricant.
 8. A tool according to claim 7 wherein said lip seal is rubber and contains solid lubricant.
 9. A tool according to claim 8 wherein said lip seal contains a plurality of layers of fibers, at least one layer being composed of porous fibers that act as a wick for liquid lubricant, and at least one other layer being composed of fibers which have a substantially greater tensile strength than said porous fibers. 